# copysign, copysignf, copysignl

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< c‎ | numeric‎ | math

Defined in header ``<math.h>`` |  |
float copysignf( float x, float y ); | (1) | (since C99)
double copysign( double x, double y ); | (2) | (since C99)
long double copysignl( long double x, long double y ); | (3) | (since C99)
Defined in header ``<tgmath.h>`` |  |
#define copysign(x, y) | (4) | (since C99)

1-3) Composes a floating-point value with the magnitude of `x` and the sign of `y`.
4) Type-generic macro: If any argument has type long double, `copysignl` is called. Otherwise, if any argument has integer type or has type double, `copysign` is called. Otherwise, `copysignf` is called.

### Parameters

x, y | - | floating-point values

### Return value

If no errors occur, the floating-point value with the magnitude of `x` and the sign of `y` is returned.

If `x` is NaN, then NaN with the sign of `y` is returned.

If `y` is -0, the result is only negative if the implementation supports the signed zero consistently in arithmetic operations.

### Error handling

This function is not subject to any errors specified in `math_errhandling`.

If the implementation supports IEEE floating-point arithmetic (IEC 60559),

- The returned value is exact (FE_INEXACT is never raised) and independent of the current rounding mode.

### Notes

`copysign` is the only portable way to manipulate the sign of a NaN value (to examine the sign of a NaN, signbit may also be used).

### Example

Run this code

    #include <math.h>
    #include <stdio.h>

    int main(void)
    {
        printf("copysign(1.0,+2.0)      = %+.1f\n", copysign(1.0,+2.0));
        printf("copysign(1.0,-2.0)      = %+.1f\n", copysign(1.0,-2.0));
        printf("copysign(INFINITY,-2.0) = %f\n",    copysign(INFINITY,-2.0));
        printf("copysign(NAN,-2.0)      = %f\n",    copysign(NAN,-2.0));
    }

Possible output:

    copysign(1.0,+2.0)      = +1.0
    copysign(1.0,-2.0)      = -1.0
    copysign(INFINITY,-2.0) = -inf
    copysign(NAN,-2.0)      = -nan

### References

- C23 standard (ISO/IEC 9899:2024):

  - 7.12.11.1 The copysign functions (p: TBD)

  - 7.25 Type-generic math <tgmath.h> (p: TBD)

  - F.10.8.1 The copysign functions (p: TBD)

- C17 standard (ISO/IEC 9899:2018):

  - 7.12.11.1 The copysign functions (p: TBD)

  - 7.25 Type-generic math <tgmath.h> (p: TBD)

  - F.10.8.1 The copysign functions (p: TBD)

- C11 standard (ISO/IEC 9899:2011):

  - 7.12.11.1 The copysign functions (p: 255)

  - 7.25 Type-generic math <tgmath.h> (p: 373-375)

  - F.10.8.1 The copysign functions (p: 529)

- C99 standard (ISO/IEC 9899:1999):

  - 7.12.11.1 The copysign functions (p: 236)

  - 7.22 Type-generic math <tgmath.h> (p: 335-337)

  - F.9.8.1 The copysign functions (p: 465)

### See also

fabsfabsffabsl (C99)(C99) | computes absolute value of a floating-point value (\(\small{|x|}\)|x|) (function)
signbit (C99) | checks if the given number is negative (function macro)
C++ documentation for copysign

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